Abstract: A rotary drill bit which is contractible to fit within a casing to permit withdrawal through the casing, and which is expandable below the casing to drill a well bore of a diameter larger than the outside diameter of the casing so as to permit the casing to follow the bit as drilling progresses to prevent the collapse of the well bore thereabove. The drill bit includes a base having pivotally mounted thereon a plurality, e.g., three, circumferentially spaced cutter arms, the cutter arms being pivotable inwardly and outwardly between retracted positions corresponding to the contracted condition of the bit and extended positions corresponding to the expanded condition of the bit. Stops are provided for preventing outward pivotal movement of the cutter arms beyond their extended positions and inward pivotal movement beyond their retracted positions, certain of these stops carrying the drilling load so that no substantial loads are applied to the pivot pin.